The rheology, microstructure, and phase behavior of dendritic and hyperbranched polymers.

摘要

In this work we seek the relationship between the microstructure of dendritic polymers and their macroscopic properties through the combined use of rheology, small-angle neutron scattering, and thermodynamic analysis. First, it was observed that the conformation of dendrimers changes dramatically as the generation number is increased, being open and swollen for the first few generations, and then more compact and dense at higher generations. This is related to increased steric crowding of the endgroups, which respond by backfolding into the molecular interior, leading to density profile that is more homogeneous than core-shell. Steric effects are also observed when comparing full dendrimers to dendrons, which have a greater dependence on solvent quality.; The conformation of dendrimers has a strong influence on their melt and solution rheology. The addition of bulky groups to the dendritic ends results in a decrease in the amount of intermolecular penetration, which serves to lower the melt viscosity. This also has a non-trivial effect on its thermal properties, including its glass transition temperature. Further, hydrogen bonding between endgroups leads to unique rheological behavior and the formation of a weak network.; The highly branched topology of dendrimers results in the exclusion of other molecules from their interior. This is observed as an increase in the excluded volume as deduced from UNIFAC correlations of dendrimer solution activity data. Further, exclusion of linear chains from dendrons in dendritic-linear diblock copolymers leads to microphase separation in the neat systems and mesoscale phase separation in blends with homopolymers.; Finally, dendrimers and HBPs are shown to be effective rheology modifiers and plasticizers. Successful viscosity modification has been demonstrated using both functionalized dendrimers and hyperbranched polymers in polystyrene, while PVC has been successfully plasticized using appropriately modified PPI dendrimers. Polymer solubility considerations were found to be critical, as the effectiveness of these materials was very dependent on the compatibility between the linear polymer and dendrimer. The knowledge gained here will be useful in the future development of novel hyperbranched polymers as nonvolatile plasticizers and processing aids.